A solar pond works upon the principle that a shallow pond placed in the sun and having a salt density gradient increasing toward the bottom of the pond will produce a usable amount of heat energy in the lower layers. The heat from these lower layers is then drawn off and generally used for either space or water heating or in certain situations electricity generation. In order to prevent the seepage of salt water from the pond which could contaminate local ground water, a liner is generally placed in the pond.
With reports indicating that temperature above 200.degree. F. have been obtained at the lower layers of some of the ponds presently in use, there is little doubt that the potential energy supply is significant if the heat can be suitably transferred out of the pond. Developing a workable and economically feasible apparatus for removing this heat has been difficult.
One early attempt to remove heat from these lower layers utilized ponds that were manufactured with inlet and outlet pipes opening into the most heated portion of the pond. By this method, the brine solution was drawn from the pond, circulated to a heat exchanger and returned to the pond. One difficulty with this system was that it was sometimes very time consuming and difficult to place the inlet and outlets in such a configuration that the movement of the brine would not disrupt the gradient within the pond. In addition, due to the fact that the brine is highly corrosive of metals, there was also an exceptional amount of wear on the piping used for the inlets and outlets and also on those portions of the heat exchanger which were in contact with the brine.
Another method of withdrawing heat from a solar pond involves the placement of a tubing on the bottom of the pond. As indicated above, where this tubing is made of metal or another corrosive material, the brine solution would cause a quick deterioration. While this method would allow for water to pass through the tubing avoiding contact with the brine solution, the positioning of the tubing was somewhat difficult. This is especially true in those situations wherein the tubing had to be removed to check for leaks or to in some way fix the passageway and the user was faced with a difficult task of trying to place the tubing back into the pond in an advantageous configuration.
In order to overcome some of the problems common to solar ponds and heat exchangers being used, the inventor began working on a new mat-type heat exchanger. One major advantage of utilizing a mat-type heat exchanger having conduits within the mat for circulation of heat exchanging liquid is the ability to provide a second layer of protection for the pond lining. By utilizing a redundant bottom lining, there is less likelihood of seepage which can contaminate ground waters. In addition, the mat can simply be placed on the surface of the pond where, due to the combined weight of the mat and heat exchange fluid, it will sink to the bottom of the pond with the predetermined conduit configurations intact as part of the mat. By manufacturing the mat out of a non-corrosive material, it is also possible to avoid the corroding effects of the brine solution.
While there are several advantages to the use of such a mat as a heat exchanger, one significant difficulty arose in that the mat and pond lining would form an adhesion which made removal of the mat difficult, especially without disrupting the salt gradient. The present invention overcomes this difficulty.
It is therefore an object of this invention to provide a heat exchanger which would aid in preventing seepage from the pond.
Another object of this invention is to provide a heat exchanger which can easily be separated and removed from the bottom of the pond.
Yet another object of this invention is to provide a heat exchanger which is easy to place in the pond with the heat exchanging conduits in the preferred and predetermined position.
Another object is to provide a heat exchanger which is not adversely affected by the brine solution in the pond.
Still another object of this invention is to provide a heat exchanger, the use of which does not disrupt the salt gradient within the pond.
Another object of this invention is to provide a heat exchanger which is economical to manufacture and operate.
Briefly described, the present invention comprises, in its preferred embodiment, an improved heat exchanger mat consisting of a flexible membrane having at least two conduits integrally associated therewith. The first conduit is utilized for heat exchange in that it is designed for the reception, circulation and discharge of a heat exchanging fluid. Heat from the solar pond is absorbed by the heat exchanging fluid as it circulates through the conduit. The first conduit generally has one inlet and one outlet so that the heated fluid can be recovered and transported to wherever it is to perform its thermal function. The second conduit has one inlet and a plurality of outlets located on one side of the membrane so that any medium, usually fluid, injected into the second conduit will exit through the openings thus forming a fluid layer beneath the mat that dislodges the mat from the bottom of the pond and from the solar pond liner and allows it to slide edgewise along the surface of the liner and out of the pond without disrupting the pond's thermal gradient.
Also briefly described, the present invention further consists of a method for removing a heat exchanger mat from the bottom of the solar pond without disturbing the thermal gradient. To accomplish this end, the heat exchanger mat is separated from the bottom of the pond by introducing a layer of separating medium between the mat and the pond bottom. The separating medium is introduced from the heat exchanger mat via a dislodging conduit having a plurality of outlets located on one side of the mat. If the solar pond contains a pond liner, the dislodging conduit may be located either in the heat exchanger mat or the liner. Retrieval cords, attached to the mat, are used to draw the mat sideways out of the pond.
The invention also encompasses a solar pond incorporating the above described features.